1. Field of the Invention
The present invention relates to a control device and a control method for a generator-motor which is mainly mounted on a vehicle and operates also as a motor when starting an engine and assisting torque.
2. Description of the Related Art
In recent years, for the purpose of improving fuel consumption and adapting to environmental standards, there has been developed a vehicle having a generator-motor mounted thereon to employ so-called idle reduction, which stops an engine when the vehicle stops and restarts the engine when starting the vehicle. The generator-motor for such a vehicle is required to be small in size, low in cost, and high in efficiency, and hence a current reducing resistor is not often provided between a power source and the generator-motor (see, for example, Japanese Patent Application Laid-open No. 2003-113763).
However, the conventional technology has the following problems.
In such an idle reduction system using a generator-motor, there is a case where the generator-motor is driven with a high voltage in order to secure torque necessary for starting an engine. In this case, there is a problem in that a current value immediately after the driving exceeds a permissible value of the generator-motor. Further, if the number of parallel-connected semiconductors is increased in order to increase the current permissible value of the generator-motor, the size and cost increase. In addition, an excess current leads to an excess torque, and hence there is a problem in that a belt slips and energy accumulated by power generation becomes waste.